Sen. Elizabeth Warren hit back on Wednesday at President Donald Trump for repeatedly ridiculing her as “Pocahontas,” saying he has tried to make Native American history “the butt of a joke” while also defending herself against criticism that she hasn’t been forthright about her heritage.

“We have a president who can’t make it through a ceremony honoring Native American war heroes without reducing Native history, Native culture, Native people to the butt of a joke,” Warren, a Massachusetts Democrat who is considered a possible presidential candidate, said during an unscheduled speech at the National Congress of American Indians in Washington. “The joke, I guess, is supposed to be on me.”

Warren, who Trump has claimed “made up her heritage” to advance her career, also addressed her family background, explaining that her mother was part Native American, but insisted she never tried to use it to her advantage.

“I get why some people think there’s hay to be made here. You won’t find my family members on any rolls, and I’m not enrolled in a tribe,” Warren said. “And I want to make something clear. I respect that distinction.”

She added, “I understand that tribal membership is determined by tribes — and only by tribes. I never used my family tree to get a break or get ahead. I never used it to advance my career. But I want to make something else clear, too: My parents were real people.”

The speech by Warren highlighted that she is prepared to take on Trump over his insults, inflammatory rhetoric and contentious policies. Her remarks also show she is working to shore up possible political weaknesses by addressing her family background and charges she misrepresented it to gain unfair advantage in her career.

Warren said Wednesday that her mother’s family was “part Native American” and that her parents eloped in 1932 because her father’s family opposed the relationship. She told the story of their difficult life together and vowed that she would not let Trump demean their legacy.

“They’re gone, but the love they shared, the struggles they endured, the family they built, and the story they lived will always be a part of me. And no one — not even the president of the United States — will ever take that part of me away,” she said.

And while Warren acknowledged that “our country’s disrespect of Native people didn’t start with President Trump,” she promised that whenever he — or anyone else — insults her family, she will “use it to lift up the story” of other Native American families and communities.

Trump began using the “Pocahontas” slur to attack Warren during the 2016 campaign, saying that June that Warren had “made up her heritage, which I think is racist.”

“I think she’s a racist, actually because what she did was very racist,” Trump said then.

Warren faced similar attacks about her heritage during her 2012 Senate race against Republican Scott Brown. Brown claimed she had dishonestly listed herself as Native American while working as a faculty member at the University of Pennsylvania and Harvard to help her career.

Warren denied the charges at the time.

Trump, meanwhile, has continued his use of the derogatory nickname, including during a White House event in November honoring Native American veterans.